The present invention pertains to the synthesis of unsaturated amides and 2-alkenyl oxazolines.
2-Isopropenyl oxazoline and the related 2-vinyl oxazolines are a class of known compounds whose properties, synthesis and utilities are described in Tomalia, "Reactive Heterocyclic Monomers", 2Functional Monomers 71-89 (R. Yocum & E. Nyquist Ed. 1974). 2-vinyl oxazolines can be polymerized to form poly-2-vinyl oxazolines, which are hydrolyzed to form useful ion-exchange resins.
Three references by de Benneville et al. disclose that 4,4-alkyl-2-vinyl- and 4,4-alkyl-2-isopropenyl oxazolines are prepared by the reaction of an aminoalkanol with acrylic or methacrylic acid in the presence of alkyl titanate or aluminum alkoxides. de Benneville et al., Oxazine and Oxazoline Derivatives, U.S. Pat. No. 2,831,858 (Apr. 22, 1958): de Benneville et al., Oxazine and Oxazoline Polymers, U.S. Pat. No. 2,897,182 (July 28, 1959): de Benneville et al., "Transesterification of Methyl Methacrylate with Aminoalcohols. Preparation of Primary Aminoalkyl Methacrylate and 2-Isopropenyl-4,4-dimethyl Oxazoline", 23 J. Org. Chem. 1355 (1958). The process reported in those references is not functional unless the aminoalkanol contains two alkyl substituents bonded to the carbon which bears the amine group. The process, therefore, can only form 4,4-disubstituted oxazolines. The disubstituted oxazolines do not hydrolyze as effectively as unsubstituted oxazolines. The description of the process shows that alkali metal alkoxides are not effective catalysts for the process shown.
Two references disclose that 2-vinyl oxazoline can be formed by the reaction and subsequent pyrolysis of 1,2-dicyanocyclobutane with two equivalents of an aminoethanol. Arit, Process for Preparing 2-Vinyl Oxazolines, U.S. Pat. No. 3,962,270 (June 8, 1976): Arit, Process for Preparing 2-Vinyl Oxazolines, U.S. Pat. No. 4,045,447 (Aug. 30, 1977).
It is also known to prepare 2-ethyl oxazoline by first amidating propionic acid with ethanolamine and second dehydrating the resulting amide in the presence of a catalyst. Kaiser, Process for Preparing 2-Oxazolines, U.S. Pat. No. 4,203,900 (May 20, 1980). The resulting ethyl oxazoline is converted by reaction with formaldehyde to 2-(1-hydroxyisopropyl) oxazoline. That intermediate can be converted to isopropenyl oxazoline by dehydration in the presence of a strong base.
The reaction described by de Benneville et al. does not provide a method to make oxazolines without alkyl substituents in both 4 positions. Other known reactions require multiple steps and/or expensive reagents. What is needed is a simple process to form either monosubstituted or unsubstituted 2-(1-alkylalkenyl)oxazolines such as isopropenyl oxazoline from readily available materials with a small number of steps.